Construction in insulated housing for terminating shielded high voltage cable



NOV. 14, 1967 R R BROWN E 3,352,962

CONSTRUCTION IN INSULATED HOUSING FOR TERMINATING SHIELDED HIGH VOLTAGE CABLE Filed Jan. 18. 1965 INVENTORS ROBERT R. BROWN LEONARD E. DAUM ATTORNEY United States Patent Office 3,352,962 Patented Nov. 14, 1967 3,352,962 CONSTRUCTION IN INSULATED HOUSING FOR TERMINATING SHIELDED HIGH VOLTAGE CABLE Robert R. Brown, Bernardsville, and Leonard E. Daum,

Morristown, N.J., assignors to Elastic Stop Nut Corporation of America, Union, N.J., a corporation of New Jerse) Filed Jan. 18, 1965, Ser. No. 426,338 Claims. (Cl. 174-73) ABSTRACT OF THE DISCLOSURE An improved construction for shielded and insulated housings or stress relief cones for terminating shielded cables, the construction including an inner member of insulating elastomeric material and an outer member of electrically conductive elastomeric material, the outer member having an axial bore including portions for engaging the insulation and the shield of the cable and having an undercut groove between the portions of the bore for assuring intimate contact between the outer member and the insulation of the cable and confining any air trapped between the outer member and the cable to a cavity established by the undercut groove so that any such trapped air is surrounded by the electrically conductive material of the outer member and by the shield of the cable to reduce the electrical stresses across the trapped air and eliminate damaging corona.

This invention relates to shielded electrical terminals, and more particularly to shielded and insulated housings or stress relief cones for terminating or connecting cables having a covering of insulation for the conductor thereof, and an electrically conductive shield surrounding the covering.

In preparing for terminating or connecting such a cable, a portion of the shield is removed to bare the insulation covering and leave a terminal rim in the shield. The housing or stress relief cone has a bore including a portion having an internal diameter for receiving and engaging the bared insulation, and a portion of relatively larger internal diameter for receiving the terminal portion of the conductive shield. The stepped diameters tend to form a pocket or cavity to trap air in contact with the 'bared insulation. Such trapped air tends to break down and form a corona damaging to all adjacent material, and generate noise objectionable to radio reception.

It is therefore an important object of the present invention to provide a housing or stress relief cone having a construction which will prevent damaging corona as a result of such an air pocket by assuring intimate contact of the stress relief material with the insulation at the inner edge of the terminal rim of the conductive shield as well as with the terminal rim itself.

According to the present invention the housing or stress relief cone is provided with an outer member of electrically conductive elastomeric material having an outer hollow engaging the shield and an inner hollow engaging the insulation, and an undercut groove forming a cavity and establishing an inwardly tapering shoulder between said hollows for assuring intimate contact between the stress relief material and the insulation of the cable along the inner hollow and for contacting at least the inner edge of said terminal rim of said conductive shield. Axial thrust in applying the stress cone increases the contact between the shoulder and the terminal rim to a land which may cover the entire rim. At least any air trapped between the outer member and the cable is outside of the contacting surfaces of the outer member and the cable insulation and within the cavity so as to be surrounded by conductive material with suificient electrical conductivity to control the electrical stresses arising at the termination of the shielded cable.

Furthermore the outer hollow is relieved radially outwardly to provide an inner end larger than the exterior end, to prevent separation of the inner hollow from intimate contact with the insulation of the cable by dilation of the inner end of the outer hollow in response to the reception of the shield within the outer hollow.

In the drawing:

The single figure is a vertical axial section through a cable provided with a stress relief cone according to a preferred embodiment of the present invention.

The cable 10 shown comprises an electrical conductor 12 which may be stranded or solid metal wire such as copper or aluminum, and provided with an insulating covering, preferably a solid tube 14, and an electrically conductive shield 16. A portion of the shield is cut oif to expose a predetermined length of the insulation 14 and leaving a terminal rim 18 for the shield. A portion of the insulating covering is skived at 19 to expose a given length of conductor 12.

In order to attain electrical continuity in the shield and preserve adequate electrical insulation between the continued shield and the exposed conductor, an insulating housing 20 is applied to the terminus of the cable 10. Housing 20 has an inner member shown in the form of an inner cone 22 of resilient material with an axial bore having a cylindrical portion 24. The relative diameters of the portion 24 and the insulating cover 14 are such that the covering may be inserted into the portion 24 by hand, the resilient property of the inner cone 22 permitting the cone to be radially expansible, thereby allowing a slight dilation of the internal surface of the portion 24 of the inner cone to admit the insulation 14. Thus, the portion 24 firmly grips the exposed length of the covering 14 in an interference fit. The tight fit along the exposed length of insulation increases the dielectric strength of the creep path along the insulation covering between the exposed conductor and the shield to assure that current will not pass between the conductor and the shield along the covering.

In order to electrically continue the shield, an outer member shown in the form of an outer cone 26 of electrically conductive resilient material surrounds the inner cone 22 and is contiguous therewith over a portion of the length thereof. Between the inner cone 22 and the shield terminal rim 18, the axial bore provides the outer cone 26 with an inner hollow 28, forming an extension of the portion 24 and similarly receiving the insulation 14. Extending axially beyond the shield outer cone 26 is a sleeve 30 within which the axial bore establishes an outer hollow 32 which is relieved to a larger diameter at the inner end thereof. The relieved portion of hollow 32 is formed by an undercut groove, which establishes a cavity 36 and forms an inwardly tapering shoulder 34 between the hollows 28 and 32, for contacting the inner edge of the terminal rim 18. The undercut groove and tapering shoulder assure intimate contact between the inner hollow 28 and the exposed insulation of the cable so that no air is trapped between the outer cone 26 and the insulation 14 of the cable along the inner hollow 28.

The relative normal diameters of the internal surfaces of hollows 28 and 32 and the corresponding external surfaces of the shield 16 and insulation 14 are such that the shield and covering may be inserted thereinto by hand. Axial thrust in applying the housing 20 increases the contact of the shoulder 34 with the rim 18 to a land, which may cover the entire rim, so that intimate contact between the electrically conductive elastomeric material of the outer cone 26 and the insulation 14 is 3 assured allthe way up to the rim 18, despite the fact that rim 18. may have irregularities as a. result of cutting the shield to expose the insulation. Thus, all air is driven from between the inner hollow 28 and the insulation 14, and any air trapped at thisvicinity is at least outside ofthe insulation 14, and lies within cavity 36 surrounded by conductive material with sufiicient electrical conductivity to control the. electrical stresses arising at the termination of the shielded cable.

The resilient property of the outer cone 26 permits the parts thereof to be readily expansible, thereby allowing a slight dilation of the internal surfaces of hollows 28- and 32 to, admit the shield 16 and establish an interference fit between the shield and the surface 32 to attain an effective electrical connection between the shield andsleeve 30, and an interference fit between the insulation 14 and the internal surface of hollow 28. Additionally, the interference fit between the shield and the internal surface of hollow 32, as well as theinterference fit between the covering and the internal surface of hollow 28, provide a water tight seal along these overlapping surfaces to prevent water from approaching the electrical conductor 12 along. these surfaces. Thus the outer cone. 26 becomes, in effect, av shield for portions of the cable and the conductor which extend beyond the terminus 18 of the shield 16.

It is important that adequate electrical insulation be provided between the shield and the conductor at all points along the housing, and it is the function of the inner cone to provide the necessary insulation. -It is also necessary to assure that the transition from the shield 16 to the shield provided by the outer cone 26 be accomplished without a deleterious concentration of electrical stresses along any portion of the housing 20.

The outer cone 26 terminates in a bell flaring outwardly from the shield terminal rim 18 toward the cable terminal end with a convex surface of revolution 27, and the inner cone 22 has a mating concave surface of revolution 23 joined thereto bymolding.

.Both the inner cone 22 and the outer cone 26 are fabricated of elastomeric material, the inner cone being an electrically insulating elastomer, while the outer cone is an electrically conductive elastomer. The two cones are contiguous to form acomposite housing joined in a single assembly. The cones are molded together so that the juncture between the cones is continuous and void free to enable the electrical stresses to be kept with? in control along thelength of the housing.

What we claim is:

1. A composite housing for terminating a high voltage cable, said cable having an electrical conductor, insula! tion covering said conductor, and an electrically conduc tive shield surrounding the insulation, a portion of said insulation being. exposed, said shield having a terminal rim; said housing comprisingan inner member molded of electrically insulating elastomeric material having a resilient portion for cooperating with theexposed insulation to firmly grip the same to increase the dielectric strength of the creep path along theinsulation; and an outer member of resilient electrically conductive elastomeric material.

molded around said inner member aong at least-a portion of the length of said inner member and havinga portion for cooperating with said shield to attain an effectual electrical connection therewith; said members being contiguous andjoined by molding in a single assembly and the junction between saidmembers being continuous and void free; said outer member having an outer hollow for engaging said shield and an inner hollow for engaging said insulation, and an undercut groove establishing a cavity anda shoulder in said outer member between said hollows, said shoulder tapering inwardly from said outer hollow to said inner hollow, in a direction away from said inner member for allowing intimate contact between the exposed insulation of the cable and the inner member and for, contacting the inner edge of saidterrninal rim of said shield along at least a portion of the shoulder such that any air trapped within the housing will be confined to said cavity and surrounded by electrically conductive materialhaving sufficient electrical conductivity to reduce the electrical stresses across the trapped air.

2. A composite housing for terminating a high voltage cable, said cable having an electrical conductor, insulation covering said conductor, and an electrically conductive shield surrounding said insulation, a portion of said insulation being exposed, said shield having a terminal rim; said housing comprising an inner member molded of electrically insulating elastomeric material having a re silient portion for cooperating, with the exposed insulation to firmly grip the same to increase the dielectric strength of the creep path along the insulation; and an outer member of resilient electrically conductive elastomeric material molded around said inner member along at least a portion of the length of said inner member and having a portion for cooperating with said shield to attain an effectual electrical connection therewith; said members being contiguous and joined by molding in a single assembly and the junction between said members being continuous and void free; said outer member having an outer hollow including at least a portion for engaging said shield and aninner hollow for engaging said insulation from the terminal rim of the shield to the inner member, and an undercut groove establishing a cavity in said outer member at the juncture of the inner and outer hollows such that said outer hollow is relieved to provide an inner end of relatively larger diameter than the diameter of the shield-engaging portion to prevent the dilation of said inner end of said outer hollow from lifting said inner hollow out of intimate contact with said insulation and confine any air trapped within the housing to said cavity wherein suchair will be surrounded by electrically conductive material having sufiicient electrical conductivity to reduce the electrical stresses across the trapped air.

3. A prefabricated stress relief cone for the terminal end of a high voltage ground shield cable to prevent electrical breakdown of such cable, said cable comprising a central conductor, a tube of insulation surrounding said central conductor, and a ground shield jacket of conductive material surrounding said insulation tube, said ground shield jacket being cut back from the terminal end of said cable to bare a terminal portion of said insulation tube andform a rim at the cut end of aid ground shield jacket, said stress relief cone having an axial bore for. receiving said baredterminal portion of said insulation tube andincluding a first portion for engaging said insulation tube in intimate contact from the rim of the shield jacket along the insulation tube, said stress relief cone having a sleeve portion of electrically conductive materialextending rearwardy in a direction away from the cable terminal end with an enlarged secondportion of said axial bore-in said sleeve portion for receiving and overlyingthe terminal portion of said ground shield jacket beyond said rim, and an undercut groove between said first-and second axial bore portions establishing a cavity and an annular shoulder for abutting the inner edge of said rim, said shoulder being inclined outwardly away from said axial bore to said undercut groove, said undercut groove andsaid shoulder defining the profile of said cavity, which profile froms an acute angle in all axial planespassing through said conductor such that any air trapped within the stress relief cone will be confined to saidlcavity and surrounded by electrically conductive material having suflicient electrical conductivity to reduce the electrical stresses across the trapped air.

4. A prefabricated stress relief cone for the terminal 'end of a high voltage ground shielded cable to prevent electrical breakdown of such cable, said cable comprising acentral conductor, a tube of solid insulation surrounding said central conductor, and a ground shield jacket of conductive material surrounding said insulation tube, said ground shield jacketbeing cut back from the end of said cable to bare a terminal portion of said solid insulation tube and expose a cut end of said ground shield jacket, said stress relief cone comprising an inner cone of insulation and an outer cone of electrically conductive material in tandem and having a common axial bore for receiving said bared terminal portion of said solid insulation tube and including a first portion for receiving at least a portion of said insulation tube, said outer cone having a sleeve portion of electrically conductive material extending rearwardly with an enlarged second portion of said axial bore in said sleeve portion for receiving and overlying the terminal portion of said ground shield jacket, an undercut groove between said first and second portions of the axial bore and diverging radially outwardly in the direction from the second portion toward the first portion of said axial bore, said undercut groove establishing a cavity and an annular shoulder for abutting said cut end of said ground shield jacket and inclined radially outwardly away from said axial bore to said undercut groove, said undercut groove and said shoulder defining the profile of said cavity, which profile forms an acute angle in all axial planes passing through said conductor such that said first portion of the bore Will be in intimate contact with said bared portion of said insulation tube between the cut end of the shield jacket and the inner cone and any air trapped within the stress relief cone will be confined to said cavity and surrounded by electrically conductive material having sufiicient electrical conductivity to reduce the electrical stresses across the trapped air.

5. A prefabricated stress relief cone for the terminal end of a high voltage ground shielded cable to prevent electrical breakdown of such cable, said cable comprising a central conductor, a tube of solid insulation surrounding said central conductor, and a ground shield jacket of conductive material surrounding said solid insulation tube, said ground shield jacket being cut back from the end of said cable to bare a terminal portion of said solid insulation tube and expose a cut end of said ground shield jacket; said stress relief cone comprising an inner cone of insulation and an outer cone of electrically conductive material in tandem and having a common axial bore for receiving said bared terminal portion of said solid insulation tube and including a first portion in said outer cone for receiving at least a portion of said insulation tube, said outer cone having a bell flaring outwardly from said axial bore toward the cable end with a convex surface of revolution, and said inner cone having a mating concave surface of revolution joined thereto by molding, said outer cone having a sleeve portion of electrically conductive material extending rear- Wardly therefrom with an enlarged second portion of said axial bore in said sleeve portion for receiving and overlyin the terminal portion of said ground shield jacket, an undercut groove between said first and second portions of the axial bore and diverging radially outwardly in the direction from the second portion toward the first portion of said axial bore, said undercut groove establishing a cavity and an annular shoulder for abutting said cut end of said ground shielded jacket and inclined radially outwardly away from said axial bore to said undercut groove, said undercut groove and said shoulder defining the profile of said cavity, which profile forms an acute angle in all axial planes passing through said conductor such that said first portion of the axial here will be in intimate contact with said bared portion of said insualtion tube between the cut end of the shield jacket and the inner cone and any air trapped within the stress relief cone will be confined to said cavity and surrounded by electrically conductive material having suflicient electrical conductivity to reduce the electrical stresses across the trapped air.

References Cited UNITED STATES PATENTS LARAMIE E. ASKIN, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,352 ,962 November 14 1967 Robert R. Brown et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2 line 52 strike out "shield"; column 3 line 61 for "aong" read along column 4, line 39, for "shield" read shielded line 46, for "aid" read said Signed and sealed this 3rd day of December 1968.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents Edward M. Fletcher, J r.

Attesting Officer 

1. A COMPOSITE HOUSING FOR TERMINATING A HIGH VOLTAGE CABLE, SAID CABLE HAVING AN ELECTRICAL CONDUCTOR, INSULATION COVERING SAID CONDUCTOR, AND AN ELECTRICALLY CONDUCTIVE SHIELD SURROUNDING THE INSULATION, A PORTION OF SAID INSULATION BEING EXPOSED, SAID SHIELD HAVING A TERMINAL RIM; SAID HOUSING COMPRISING AN INNER MEMBER MOLDED OF ELECTRICALLY INSULATING ELASTOMERIC MATERIAL HAVING A RESILIENT PORTION FOR COOPERATING WITH THE EXPOSED INSULATION TO FIRMLY GRIP THE SAME TO INCREASE THE DIELECTRIC STRENGTH OF THE CREEP PATH ALONG THE INSULATION; AND AN OUTER MEMBER OF RESILIENT ELECTRICALLY CONDUCTIVE ELASTOMERIC MATERIAL MOLDED AROUND SAID INNER MEMBER ALONG AT LEAST A PORTION OF THE LENGTH OF SAID INNER MEMBER AND HAVING A PORTION FOR COOPERATING WITH SAID SHIELD TO ATTAIN AN EFFECTUAL ELECTRICAL CONNECTION THEREWITH; SAID MEMBERS BEING CONTIGUOUS AND JOINED BY MOLDING IN A SINGLE ASSEMBLY AND THE JUNCTION BETWEEN SAID MEMBERS BEING CONTINUOUS AND VOID FREE; SAID OUTER MEMBER HAVING AN OUTER HOLLOW FOR ENGAGING SAID SHIELD AND AN INNER HOLLOW FOR ENGAGING SAID INSULATION, AND AN UNDERCUT GROOVE ESTABLISHING A CAVITY AND A SHOULDER IN SAID OUTER MEMBER BETWEEN SAID HOLLOWS, SAID SHOULDER TAPERING INWARDLY FROM SAID OUTER HOLLOW TO SAID INNER HOLLOW IN A DIRECTION AWAY FROM SAID INNER MEMBER FOR ALLOWING INITIMATE CONTACT BETWEEN THE EXPOSED INSULATION OF THE CABLE AND THE INNER MEMBER AND FOR CONTACTING THE INNER EDGE OF SAID TERMINAL RIM OF SAID SHIELD ALONG AT LEAST A PORTION OF THE SHOULDER SUCH THAT ANY AIR TRAPPED WITHIN THE HOUSING WILL BE CONFINED TO SAID CAVITY AND SURROUNDED BY ELECTRICALLY CONDUCTIVE MATERIAL HAVING SUFFICIENT ELECTRICAL CONDUCTIVITY TO REDUCE THE ELECTRICAL STRESSES ACROSS THE TRAPPED AIR. 